This invention relates to apparatus for fabricating wood structures, and is more particularly concerned with such apparatus especially adapted to fabricate flat floor trusses and other shallow depth trusses.
In conventional construction practice, solid wood members, such as 2 .times. 12's or the like, are used for floor joists. However, due to increased lumber costs and scarcity of long span lumber of the required dimensions, flat trusses made of less expensive lumber (e.g., 2 .times. 4's), are becoming increasingly popular for use as floor joists in place of solid wood joists. In addition to utilizing less expensive lumber, trusses are lighter weight and permit considerable labor savings because electrical wiring, plumbing and ventilation ducts may be readily routed through openings in the trusses. The trusses thus provide unobstructed surfaces at the top and bottom thereof to which ceiling or sub-floor sheathing panels may readily be nailed.
Truss fabricating apparatus, such as shown in my U.S. Pat. No. 3,866,530, has been developed for the manufacture of floor trusses. This apparatus supports wood members on stands and has two hydraulic presses mounted on carts which move automatically along a respective chord of the truss from one location therealong to another to drive nailing plates into the wood members simultaneously from above and below.
Other truss fabricating apparatus is known which may be utilized to fabricate flat floor trusses. This other apparatus utilizes a gantry structure movable along a bed on rails and having one or more platens movable toward the wood members for pressing nailing plates thereinto. In U.S. Pat. No. 3,605,608, the rails are shown to be on the outside of a fixed lower bed of reinforced concrete or the like and the gantry is shown to have an upper platen movable downwardly by means of a bell crank arrangement actuated by a hydraulic cylinder so as to drive the nailing plates into wood members supported on the bed. Here, the rails must carry the load as the upper platen engages the nailing plates on the wood members supported by the lower bed and drives the nailing plates into the wood members. This above-mentioned gantry-type apparatus, requires a substantial investment of labor and money to install, and once installed is immovable.
In U.S. Pat. No. 3,826,188, a gantry is shown movable along a track. The gantry has a lower platen at a fixed elevation and a pair of hydraulic cylinder units mounted on trolleys movable along an upper beam of the gantry above the lower platen for being positioned over a nailing plate location so as to press the nailing plate at that location into the wood members. The wood members are supported on a table above the lower platen. This table is supported by pivotal stands which are moved out of the way by the lower platen as the gantry travels along its tracks. This last-mentioned apparatus requires that the gantry be positioned along the truss at nailing plate locations and that the truss trolleys be adjusted along the gantry at the nailing plate locations. This is complicated and requires time which slows production.
In another known type of gantry truss fabricating machine, the wood members are supported on the upper surface of a table and a press frame is movable along the table to press nailing plates into the wood members. The table has an elongate beam at each side of the table with clearance below the beams and with the top of the table forming a bed for supporting the wood members. Each beam has a track on the inside of its web. The press frame has a carriage movable along the tracks below the bed, the carriage constituting a lower platen engageable with the bottom of the bed. The press frame further has an upper platen positioned above the table and a base below the carriage. The base is interconnected to the carriage by a pair of hydraulic cylinders. These hydraulic cylinders are actuable to open and close the upper and lower platens so as to bring the upper platen into engagement with the nailing plates positioned on the upper faces of the wood members and to bring the lower platen into engagement with the bottom of the table thereby to drive the nailing plates into the wood members. The carriage is power driven for movement along the tracks and is stopped at each nailing plate location along the truss being formed to drive the nailing plates into the wood members.
As this above-mentioned press frame is moved from nailing plate location to nailing plate location along the truss, it tends to rock in longitudinal direction of the table on its rollers as it is accelerated and decelerated. This tendency to rock may be so severe that it shakes the table and displaces or moves out of position the nailing plates pre-positioned on upper faces of wood members prior to their being driven into the wood members. In order to avoid this serious problem of displacing the nailing plates from their pre-positioned locations, users of this prior art machine have employed an individual manual hammering step on each nailing plate prior to pressing so as to temporarily retain them in their desired locations on the wood members and to thus prevent their being dislocated by the tendency by the press frame to rock as it is sequentially moved from one nailing plate location to another.